This invention pertains to a rotary tube cleaning system and method for remotely cleaning the inside of elongated small diameter tubes. It pertains particularly to such a tube cleaning system and method for remotely cleaning small diameter thimble tubes such as those used in reactors of nuclear power plants.
During operation of nuclear reactors, it is necessary to periodically monitor the level of radioactivity existing in the core of the reactor. For this purpose, a series of thimble tubes are provided which extend from a convenient external location into the reactor. These thimble tubes are closed at their inner or reactor ends and are open at their inlet ends to provide for insertion of a nuclear monitoring probe device into the reactor for measuring radioactive flux throughout the reactor core. It has been found that over time undesirable deposits can form in these small diameter thimble tubes and interfere with passage of the probe device into the reactor. To correct this serious problem without disassembly of the probe tubes, which are highly radioactive, a remotely operated tube cleaning device is needed for removing the undesired deposits in the thimble tubes. However, because of the relatively small inner diameter of the tubes (0.20-0.25 inch) and remote location of the blockages, e.g. about 85 feet from the thimble tube open end, and the radioactive environment which is involved, such tube cleaning operation is dificult to accomplish reliably and safely. Thus, a suitable solution to this tube blockage problem by using a remotely operated rotary tube cleaning system and method has been needed in the nuclear power industry.
Some devices and systems for remote cleaning of tubes by rotary devices have been developed and disclosed in the prior art. For example, U.S. Pat. No. 2,679,061 to Baker discloses a rotary tube cleaner having a tool attached to the end of a flexible hollow shaft driven by a motor and arranged for flow of a cooling liquid through a casing surrounding the shaft. U.S. Pat. No. 3,354,490 to Masters et al discloses a boiler tube cleaning apparatus using a scraper brush attached to a flexible shaft and fed forward by a positioned ejector unit. Also, U.S. Pat. No. 4,326,317 to Smith et al discloses a rotary tube cleaning apparatus for use in cleaning and flushing heat exchanger tubes of nuclear steam generators. However, because of the deficiencies associated with the known prior art, an improved tube cleaning system and method for remotely cleaning out deposits from long small diameter tubes is needed, and have been developed and provided by the present invention.